Capacitors and methods of forming capacitors

ABSTRACT

The invention includes methods of forming capacitors and capacitor constructions. In one implementation, a method of forming a capacitor includes forming a first capacitor electrode. A first layer of a first capacitor dielectric material is formed over the first capacitor electrode. A second layer of the first capacitor dielectric material is formed on the first layer. A second capacitor electrode is formed over the second layer of the first capacitor dielectric material. A capacitor in accordance with an implementation of the invention includes a pair of capacitor electrodes having capacitor dielectric material therebetween comprising a composite of two immediately juxtaposed and contacting, yet discrete, layers of the same capacitor dielectric material.

TECHNICAL FIELD

[0001] This invention relates to capacitors and to methods of formingcapacitors.

BACKGROUND OF THE INVENTION

[0002] Typical capacitors comprise a pair of conductive electrodesspaced apart by intervening capacitor dielectric material. As integratedcircuitry becomes denser and as individual electronic components such ascapacitors get smaller, integrated circuitry fabricators face thechallenge of developing capacitor constructions and materials whichachieve desired capacitance despite the decreasing size. Examplematerials under consideration for capacitor dielectric layers includetitanates and tantalum pentoxide. These and other capacitor dielectriclayer materials can occur in crystalline and in amorphous phases.

[0003] It is generally known that the capacitance of dielectricmaterials such as these can, at least initially, be increased from theiras-deposited form by annealing. Such annealing can promotecrystallization, re-crystallization or crystal realignment which canfacilitate increase in capacitance and reduction in current leakagethrough the material. However, such annealing can also cause singlecrystals to be formed in the dielectric layer which in essence extendentirely through the dielectric layer between the layer's opposingsurfaces. Annealing or crystal formation to this degree can undesirablyhave the effect of increasing current leakage. This is primarily due tocontinuous paths being provided by the continuous grain boundaries forcurrent leakage from one side of the layer to the other. It would bedesirable to improve upon these adverse characteristics of capacitordielectric layer materials.

SUMMARY OF THE INVENTION

[0004] The invention in one aspect includes methods of formingcapacitors and to capacitor constructions. In one implementation, amethod of forming a capacitor includes forming a first capacitorelectrode. A first layer of a first capacitor dielectric material isformed over the first capacitor electrode. A second layer of the firstcapacitor dielectric material is formed on the first layer. A secondcapacitor electrode is formed over the second layer of the firstcapacitor dielectric material. In accordance with anotherimplementation, the first layer comprises a first titanate compoundcomprising capacitor dielectric material and the second layer comprisesa different second titanate compound comprising capacitor dielectricmaterial. A capacitor in accordance with an implementation of theinvention includes a pair of capacitor electrodes having capacitordielectric material therebetween comprising a composite of twoimmediately juxtaposed and contacting, yet discrete, layers of the samecapacitor dielectric material. A capacitor in accordance with anotherimplementation includes a pair of capacitor electrodes having capacitordielectric material therebetween comprising a composite of twoimmediately juxtaposed and contacting, yet discrete, layers of twodifferent capacitor dielectric materials, said s two capacitordielectric materials including two different titanate compounds. Acapacitor in accordance with still another implementation includes apair of capacitor electrodes having capacitor dielectric materialtherebetween comprising a composite of two immediately juxtaposed andcontacting, yet discrete, layers of two different capacitor dielectricmaterials, one of the two different materials comprising a titanatecompound and the other comprising Ta₂O₅.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

[0006]FIG. 1 is a diagrammatic sectional view of a wafer fragment at oneprocessing step in accordance with the invention.

[0007]FIG. 2 is a view of the FIG. 1 wafer fragment at a step subsequentto that shown by FIG. 1.

[0008]FIG. 3 is a view of the FIG. 1 wafer at a processing stepsubsequent to that shown by FIG. 2.

[0009]FIG. 4 is a view of the FIG. 1 wafer at a processing stepsubsequent to that shown by FIG. 3.

[0010]FIG. 5 is a view of the FIG. 1 wafer at a processing stepsubsequent to that shown by FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] This disclosure of the invention is submitted in furtherance ofthe constitutional purposes of the U.S. Patent Laws “to promote theprogress of science and useful arts” (Article 1, Section 8).

[0012] A semiconductor wafer in process in accordance with one aspect ofthe invention is indicated in FIG. 1 with reference numeral 10. Suchcomprises a semiconductive substrate in the form of a bulkmonocrystalline silicon substrate 12. In the context of this document,the term “semiconductive substrate” is defined to mean any constructioncomprising semiconductive material, including, but not limited to, bulksemiconductive materials such as a semiconductive wafer (either alone orin assemblies comprising other materials thereon), and semiconductivematerial layers (either alone or in assemblies comprising othermaterials). The term “substrate” refers to any supporting structure,including, but not limited to, the semiconductive substrates describedabove. A first capacitor electrode 16 is formed over substrate 12.Exemplary materials include conductively doped polysilicon or TiN. Anexemplary thickness for layer 16 is from 100 Angstroms to 1500Angstroms.

[0013] A first layer 18 of a first capacitor dielectric material isformed over first capacitor electrode 16. Exemplary and preferredmaterials include barium strontium titanate (BST), strontium titanate(ST), strontium bismuth titanate (SBT), lead lanthanate zirconiatitanate (PLTZ), Ta₂O₅, and mixtures thereof. The preferred method ofdepositing layer 18 is by chemical vapor deposition. Layer 18 asinitially formed can be either crystalline or amorphous, with an initialamorphous structure being preferred and shown in the fabrication of acapacitor dielectric layer in accordance with this aspect of theinvention. Regardless, first layer 18 of first capacitor dielectricmaterial is preferably subsequently annealed at a temperature of atleast 300° C. for a time period sufficient to achieve a selectedcrystalline structure intended to densify and facilitate capacitiveproperties of such material (FIG. 2). Exemplary anneal conditionsinclude a temperature range of from about 300° C. to about 1200° C. at apressure of from about 2 mTorr to about 5 atm for a treatment time ofanywhere from about 1 minute to 2 hours. Unfortunately as describedabove with respect to the prior art, such annealing can cause sufficientrecrystallization to form singular grains at various locationsthroughout layer 18 having grain boundaries which extend from onesurface of the layer to the other, as shown.

[0014] Referring to FIG. 3, a second layer 20 of the same firstcapacitor dielectric material of layer 18 is formed on first layer 18after the preferred layer 18 annealing. Second layer 20 is alsopreferably chemical vapor deposited, and can initially be formed to beamorphous or crystalline. Preferably, it is initially formed to beamorphous as shown. Further, the thickness of first layer 18 of thefirst material is preferably chosen to be from about 10% to about 90% ofthe finished combined thickness of first layer 18 and second layer 20.An exemplary thickness range for the combination of layers 18 and 20 isfrom 60 Angstroms to 1000 Angstroms. By way of example only where thematerial of layers 18 and 20 comprises BST, an example thickness foreach layer 18 and 20 is 150 Angstroms.

[0015] Referring to FIG. 4, a second capacitor electrode 22 is formedover second layer 20 of the first capacitor dielectric material. Anexemplary thickness range for electrode 22 is from 100 Angstroms to 2500Angstroms. Further, diffusion barrier layers, if desired, can bepositioned anywhere intermediate the composite of layers 18 and 20, andfirst electrode 16 and second electrode 22. Regardless, it is mostpreferable that second layer 20 of the first material not be exposed toa temperature of 500° C. or greater before deposition of any subsequentlayer thereover. In certain instances, exposure to such temperature fora sufficient period of time could cause complete crystal realignmentrelative to the composite layer of layers 18 and 20, and undesirablyform grain boundaries which extend from the base of layer 18 clearthrough to the top of layer 20.

[0016] Electrode layer 22 and/or any intervening diffusion barrier orother layer provided over layer 20 are chosen and deposited in such away that a degree of desired stress (either tensile or compressive) willbe imparted into layer 20, either during formation/deposition orsubsequently such as when it is heated. Such stress can be impartedinherently by the electrode material during its deposition, or bychoosing deposition/forming conditions that themselves impart a desiredstress. For example, selection of temperature and pressure conditionsduring deposition/formation of the electrode layer can be selected toimpart a desired stress regardless of the electrode material beingdeposited. Alternately, the material can be chosen relative to thesecond capacitor dielectric layer to impart a desired tensile orcompressive stress. Such example materials for use with the preferredtitanates and pentoxides capacitor dielectric layers include TiN_(x),WN_(x), TaN_(x), PtRh_(x), PtRu_(x), PtIr_(x), and mixtures thereof.Further alternately, and by way of example only, the second capacitorelectrode material could be doped with a conductivity enhancing impurityduring its formation chosen to achieve a selected stress on the secondlayer of the capacitor dielectric layer.

[0017] Regardless, such stress can largely prevent completerecrystallization of the same material of layers 18 and 20. Exemplarydedicated anneal conditions include temperatures ranging from 500° C. to1000° C., and pressures ranging from 50 mTorr to 50 atmospheres.Accordingly, layer 20 is preferably ultimately annealed either with adedicated anneal step or in conjunction with other wafer processing torender it substantially crystalline in its finished composition.Regardless, the preferred capacitor construction will comprise a pair ofcapacitor electrodes having capacitor dielectric material therebetweencomprising a composite of two immediately juxtaposed and contacting, yetdiscrete, layers of the same capacitor dielectric material, as shown.

[0018] Accordingly in the above-described preferred embodiment, firstlayer 18 of the capacitor dielectric layer material is essentiallyprovided with a selected finished crystalline structure prior toformation of second layer 20 thereon. Such is achieved by thecrystallization or recrystallization anneal immediately prior toformation of layer 20. Also in the preferred embodiment, the finalcomposition of second layer 20 of the first material is also desirablyformed to be crystalline, although alternately such could remainamorphous if so initially deposited. In the preferred embodiment for acapacitor dielectric layer where both of layers 18 and 20 arecrystalline in their final form, an interface line 19 essentially formstherebetween where such discrete layers contact (FIG. 5). Interface line19 is characterized by a perceptible change in crystallinity from onelayer to the other, such as shown or evidenced in this example by asubstantial lateral shift or displacement in grain boundaries from onelayer to the other.

[0019] In accordance with another implementation of the invention, firstlayer 18 can comprise a first titanate compound and second layer 20 cancomprise a different second titanate compound. In accordance with stillanother implementation of the invention, first layer 18 can comprise onecapacitor dielectric layer material and second layer 20 can compriseanother different capacitor dielectric layer material, with one of thematerials comprising a titanate compound and the other comprising Ta₂O₅.By way of example only, example titanate compounds are those referred toabove.

[0020] Fluorine or other grain boundary passivation treatments can alsobe conducted relative to the first and second layers of materialintermediate or after such layers have been deposited. Example suchtreatments are described in our U.S. Pat. No. 5,665,611 and referencescited therein.

[0021] In compliance with the statute, the invention has been describedin language more or less specific as to structural and methodicalfeatures. It is to be understood, however, that the invention is notlimited to the specific features shown and described, since the meansherein disclosed comprise preferred forms of putting the invention intoeffect. The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1. A method of forming a capacitor comprising: forming a first capacitorelectrode; forming a first layer of a first capacitor dielectricmaterial over the first capacitor electrode; forming a second layer ofthe first capacitor dielectric material on the first layer; and forminga second capacitor electrode over the second layer of the firstcapacitor dielectric material.
 2. The method of claim 1 comprisingforming the second capacitor electrode to impart one of compressive ortensile stress on the second layer of the first capacitor dielectricmaterial during second electrode formation.
 3. The method of claim 2comprising forming the second capacitor electrode to predominatelycomprise a material selected from the group consisting of TiN_(x),WN_(x), TaN_(x), PtRh_(x), PtRu_(x), PtIr_(x), and mixtures thereof. 4.The method of claim 2 comprising doping the second capacitor electrodeduring its formation with a conductivity enhancing impurity to achieve aselected stress on the second layer of the first capacitor dielectricmaterial.
 5. The method of claim 1 comprising initially forming thefirst layer of first material to be amorphous.
 6. The method of claim 1comprising initially forming the first layer of first material to becrystalline.
 7. The method of claim 1 comprising initially forming thesecond layer of first material to be amorphous.
 8. The method of claim 1comprising initially forming the second layer of first material to becrystalline.
 9. The method of claim 1 comprising initially forming thefirst layer of first material to be amorphous, and initially forming thesecond layer of first material to be amorphous.
 10. The method of claim1 comprising initially forming the first layer of first material to beamorphous, and transforming the first layer of first material to besubstantially crystalline prior to forming the second layer of firstmaterial, the second layer of first material initially being formed tobe amorphous.
 11. The method of claim 1 comprising initially forming thefirst layer of first material to be amorphous, and transforming thefirst layer of first material to be substantially crystalline prior toforming the second layer of first material, the second layer of firstmaterial initially being formed to be amorphous, and transforming thesecond layer of first material to be substantially crystalline afterforming another layer thereover.
 12. The method of claim 11 wherein theanother layer comprises the second capacitor electrode.
 13. The methodof claim 1 comprising initially forming the first layer of firstmaterial to be amorphous, and transforming the first layer of firstmaterial to be substantially crystalline prior to forming the secondlayer of first material, the second layer of first material initiallybeing formed to be crystalline.
 14. The method of claim 1 wherein thefirst layer of first material is provided with a selected finishedcrystalline structure prior to forming the second layer of firstmaterial.
 15. The method of claim 1 wherein the first layer of firstmaterial is formed to a thickness of from 10% to 90% of a finishedcombined thickness of the first and second layers.
 16. The method ofclaim 1 comprising forming the first layer of first material to becrystalline in its final composition, and forming the second layer offirst material to be crystalline in its final composition.
 17. Themethod of claim 1 comprising forming the first layer of first materialto be crystalline in its final composition, and forming the second layerof first material to be amorphous in its final composition.
 18. A methodof forming a capacitor comprising: forming a first capacitor electrode;forming a first layer of a first capacitor dielectric material over thefirst capacitor electrode; annealing the first layer of the firstcapacitor dielectric material at a temperature of at least 300° C. for atime period sufficient to achieve a selected crystalline structure ofthe first material; after annealing the first layer, forming a secondlayer of the first capacitor dielectric material on the annealed firstlayer, the second layer of first material not being exposed to atemperature of 500° C. or greater before deposition of a subsequentlayer thereover; and forming a second capacitor electrode over thesecond layer of the first capacitor dielectric material.
 19. The methodof claim 18 wherein the first dielectric material comprises a titanatecompound.
 20. The method of claim 18 wherein the first dielectricmaterial comprises Ta₂O₅.
 21. The method of claim 18 wherein the firstdielectric material is selected from the group consisting of bariumstrontium titanate, strontium titanate, strontium bismuth titanate andlead lanthanum zirconia titanate, and mixtures thereof.
 22. The methodof claim 18 wherein the first layer is formed to a thickness of from 10%to 90% of a finished combined thickness of the first and second layers.23. The method of claim 18 comprising initially forming the first layerof first material to be amorphous.
 24. The method of claim 18 comprisinginitially forming the second layer of first material to be amorphous.25. The method of claim 18 comprising initially forming the first layerof first material to be amorphous, and initially forming the secondlayer of first material to be amorphous.
 26. The method of claim 18comprising initially forming the second layer of first material to beamorphous, and annealing the second layer of first material at atemperature of 500° C. or greater to form said second layer to becrystalline.
 27. The method of claim 26 wherein the second layerannealing occurs after forming the second capacitor electrode.
 28. Amethod of forming a capacitor comprising: forming a first capacitorelectrode; forming a first layer of a first titanate compound comprisingcapacitor dielectric material over the first capacitor electrode;forming a second layer of a second titanate compound comprisingcapacitor dielectric material on the first layer, the second titanatecompound being different from the first titanate compound; and forming asecond capacitor electrode over the second layer of second titanatecompound comprising capacitor dielectric material.
 29. The method ofclaim 28 comprising forming the second capacitor electrode to impart oneof compressive or tensile stress on the second layer of the secondtitanate compound during second electrode formation.
 30. The method ofclaim 29 comprising forming the second capacitor electrode topredominately comprise a material selected from the group consisting ofTiN_(x), WN_(x), TaN_(x), PtRh_(x), PtRu_(x), PtIr_(x), and mixturesthereof.
 31. The method of claim 29 comprising doping the secondcapacitor electrode during its formation with a conductivity enhancingimpurity to achieve a selected stress on the second layer of the secondtitanate compound.
 32. A method of forming a capacitor comprising:forming a first capacitor electrode; forming a first layer of a firsttitanate compound comprising capacitor dielectric material over thefirst capacitor electrode; annealing the first layer of the firsttitanate compound comprising capacitor dielectric material at atemperature of at least 300° C. for a time period sufficient to achievea selected crystalline structure of the first titanate compound of thefirst layer; after annealing the first layer, forming a second layer ofa second titanate compound comprising capacitor dielectric material onthe annealed first layer, the second layer not being exposed to atemperature of 500° C. or greater before deposition of a subsequentlayer thereover, the second titanate compound being different from thefirst titanate compound; and forming a second capacitor electrode overthe second layer of second titanate compound comprising capacitordielectric material.
 33. A method of forming a capacitor comprising:forming a first capacitor electrode; forming a first layer of a firstcapacitor dielectric material over the first capacitor electrode;forming a second layer of a second capacitor dielectric material on thefirst layer, one of the first and second materials comprising a titanatecompound and the other comprising Ta₂O₅; and forming a second capacitorelectrode over the second layer of second capacitor dielectric material.34. The method of claim 33 comprising forming the second capacitorelectrode to impart one of compressive or tensile stress on the secondlayer of the second capacitor dielectric material during secondelectrode formation.
 35. The method of claim 34 comprising forming thesecond capacitor electrode to predominately comprise a material selectedfrom the group consisting of TiN_(x), WN_(x), TaN_(x), PtRh_(x),PtRu_(x), PtIr_(x), and mixtures thereof.
 36. The method of claim 34comprising doping the second capacitor electrode during its formationwith a conductivity enhancing impurity to achieve a selected stress onthe second capacitor dielectric material.
 37. A method of forming acapacitor comprising: forming a first capacitor electrode; forming afirst layer of a first capacitor dielectric material over the firstcapacitor electrode; annealing the first layer of the first capacitordielectric material at a temperature of at least 300° C. for a timeperiod sufficient to achieve a selected crystalline structure of thefirst capacitor dielectric material of the first layer; after annealingthe first layer, forming a second layer of a second capacitor dielectricmaterial on the annealed first layer, the second layer not being exposedto a temperature of 500° C. or greater before deposition of a subsequentlayer thereover, one of the first and second materials comprising atitanate compound and the other comprising Ta₂O₅; and forming a secondcapacitor electrode over the second layer of second capacitor dielectricmaterial.
 38. A capacitor comprising a pair of capacitor electrodeshaving capacitor dielectric material therebetween comprising a compositeof two immediately juxtaposed and contacting, yet discrete, layers ofthe same capacitor dielectric material.
 39. The capacitor of claim 38wherein one of the discrete layers is crystalline and the other isamorphous.
 40. The capacitor of claim 38 wherein both of the discretelayers are crystalline, and comprising an interface where the discretelayers contact which is characterized by a perceptible change incrystallinity from one layer to the other.
 41. The capacitor of claim 40wherein the perceptible change in crystallinity is characterized by aperceptible lateral shift in grain boundaries from one layer to theother.
 42. The capacitor of claim 38 wherein the same capacitordielectric material comprises a titanate compound.
 43. The capacitor ofclaim 38 wherein the same capacitor dielectric material comprises Ta₂O₅.44. A capacitor comprising a pair of capacitor electrodes havingcapacitor dielectric material therebetween comprising a composite of twoimmediately juxtaposed and contacting, yet discrete, layers of twodifferent capacitor dielectric materials, said two capacitor dielectricmaterials including two different titanate compounds.
 45. A capacitorcomprising a pair of capacitor electrodes having capacitor dielectricmaterial therebetween comprising a composite of two immediatelyjuxtaposed and contacting, yet discrete, layers of two differentcapacitor dielectric materials, one of the two different materialscomprising a titanate compound and the other comprising Ta₂O₅.